The present disclosure relates to a method for adjustment of an image formation position in an image forming apparatus.
Generally, in an image forming apparatus such as an ink-jet printer or a laser printer, an image formation position (i.e., the position of an image to be formed) according to a printing unit such as a developing unit or a transfer unit is set based on a disposed position of the printing unit, and will never be changed from the set position. On the other hand, a sheet conveyance position (i.e., the position of a sheet to be conveyed) with respect to the printing unit can deviate from a preset conveyance position, due to a design tolerance or an assembly tolerance of a sheet conveyance passage, a sheet size, a loading state of sheets on a sheet feeding unit, and the like. Moreover, due to conveyance noise caused by motors, rollers, meshed gears and the like used for sheet conveyance, the sheet conveyance position can vary every time one sheet is conveyed. As above, even if the image formation position according to the printing unit is not changed, there is a possibility that a deviation occurs in the sheet conveyance position with respect to the printing unit, resulting in failing to form an image on a sheet at a proper position.
In order to solve this problem, there has heretofore been known a technique of: disposing an image sensor at a position upstream of the printing unit in a sheet conveyance direction; calculating a deviation of the sheet conveyance position, based on the center of the image formation position determined based on a disposed position of an ink head, and positions of opposite lateral edges of a sheet detected by the image sensor; and moving the image formation position in conformity to the calculated deviation.
Further, there has heretofore been known a technique of: using the above image sensor to detect an outline of a sheet being conveyed with respect to the printing unit; and using a heretofore-known masking processing to form, on a sheet, an image obtained by masking any region which is not included inside the detected outline of the sheet, thereby preventing a developer such as an ink or toner from adhering to any region other than the sheet.